The technology of converting heat to electricity, i.e., the thermoelectric conversion technology, which can effectively utilize as electric power the waste heat generated from industrial materials and civilian materials, is noted in many fields as an important technology intended for the prevention of earth warming-up.
The thermoelectric conversion device generally includes a p-type semiconductor thermoelectric conversion material and an n-type semiconductor thermoelectric conversion material sandwiched by electrodes. In order for the thermoelectric conversion materials to be highly effective, it is preferable that they have a large dimensionless performance index which is called ZT. To raise the performance index ZT, it is preferable that they have a high Seebeck coefficient, have a high electric conductivity and have a low heat conductivity.
The following is an example of related: Japanese Laid-open Patent Publication No. 2000-178070.
Satisfying a high electric conductivity and a low heat conductivity at once requires properties which are conflict depending on cases. For example, the material is nanostructured, whereby phonons are scattered at the interface of the nanostructures, and the heat conductivity can be lowered. On the other hand, the material is nanostructured, whereby, in many cases, the electric conductivity is degraded.
Accordingly, it is generally difficult to satisfy a high electric conductivity and a low heat conductivity at once, and so far, thermoelectric conversion materials having sufficiently high performance index ZT have not been found.